1. Field of the Invention
The present invention relates to a testing and annunciation device for verifying operation of the signalling system of a towed trailer. In addition, the device has provision for testing the pneumatic brakes of the trailer. The device is contained within a small wheeled cart, and enables certain electrical and mechanical systems to be monitored independently of a towing vehicle being hooked up to the trailer. The cart is maneuvered, connected, and operated manually by one person.
2. Description of the Prior Art
Freight hauling trailers drawn by over the road tractors are equipped with many signalling and safety features. Illuminated signalling lamps include brake lights, turn signals, and running lights. Safety features also include pneumatic braking systems. Trailers must be inspected periodically for operability of these signalling and safety systems. Other types of trailers such as utility trailers, recreational trailers and horse trailers also have signal lighting systems that must be periodically tested.
One way of testing and observing the systems is to connect a towing vehicle such as a tractor to the trailer. A tractor has the voltage and pneumatic sources for operating the systems. An observer can activate the various systems individually, then observe the results. This method can be quite inefficient, since it relies upon the presence of an unused tractor, and also requires time to make connections and carry out the cumbersome process of manually activating each system, then walking around the trailer to verify proper performance.
A tractor may not be available for such duty when it would be convenient to perform the safety check. A smaller and less expensive device for taking the place of the tractor would serve well as a replacement, and a number of such devices are proposed in the prior art.
U.S. Pat. No. 3,663,939, issued to Hans Olsson on May 16, 1972, discloses a device insertable in series into the combined wiring of a tractor and its trailer. This device requires the presence of a tractor, and does not cooperate with pneumatic or hydraulic systems.
A small diagnostic device which is directly plugged into a socket integral with a trailer is shown in U.S. Pat. No. 3,737,767, issued to Robert Slutsky on Jun. 5, 1973. This device is usable only with vehicles having a seven-conductor plug. The device cannot test marker lights independently of tail lights, as can the present invention, and, because it dedicates only one indicator to turn signals, cannot readily monitor a four way flashing function.
U.S. Pat. No. 4,547,722, issued to Thomas J. Sarlo on Oct. 15, 1985, describes a diagnostic device mounted in a wheeled cart. This device is also limited to testing vehicles having the particular type of receptacle provided for.
A diagnostic device for testing braking systems is set forth in U.S. Pat. No. 4,70,354, issued to Anton Knestel on Jun. 14, 1988. This device requires rollers which contact the vehicle wheels. Rollers and monitoring of road wheels are not involved in the present invention.
A circuit for diagnosing operability of a trailer's electrical system is shown in U.S. Pat. No. 5,095,276, issued to James C. Nepil on Mar. 10, 1992. This circuit is considerably more complicated than that of the present invention, while not providing the versatility of the present invention.
The prior art devices are particularly intended for use with trailers for over the road tractor and trailer combinations, and have electrical interface components specifically found on such combinations. They lack the ability to be compatible with a variety of receptacles or electrical interface components. Also, the prior art devices having electrical diagnostic circuits have no provision for testing pneumatic braking systems.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.